Đáp án:
$a)2\sqrt{75}-3\sqrt{27}-\dfrac{1}{2}\sqrt{12}+2\sqrt{108}$
$=2\sqrt{5^2.3}-3\sqrt{3^2.3}-\dfrac{1}{2}\sqrt{2^2.3}+2\sqrt{6^2.3}$
$=10\sqrt{3}-9\sqrt{3}-\sqrt{3}+12\sqrt{3}$
$=12\sqrt{3}$
$b)\left(\sqrt{\dfrac{1}{3}}-\sqrt{\dfrac{4}{3}} +2\sqrt{3}\right)÷\sqrt{3}$
$= \sqrt{\dfrac{1}{3}}÷\sqrt{3}-\sqrt{\dfrac{4}{3}}÷\sqrt{3}+2\sqrt{3}÷\sqrt{3}$
$=\dfrac{1}{3}-\dfrac{2}{3}+2$
$=\dfrac{5}{3}$
